John McGrath: Mariners gaining because of others’ attrition

Going into the second of three “Border War” games against a Toronto Blue Jays team that has brought most of the population of Western Canada with it to Safeco Field this week, the Seattle Mariners were able to boast the American League’s best trio of starting pitchers.

The effectiveness of Cy Young Award favorite Felix Hernandez, along with Hisashi Iwakuma and Chris Young, helps explain why the Mariners could become the first American League pitching staff since the 1974 world champion Oakland A’s to finish a season with a staff ERA under 3.00.

But the Mariners also rank among baseball’s leaders in a pitching category that, while obscure, is as important as any traditional statistic: Fewest Reasons for the General Manager to Seek Waiver Wire Help During the Stretch Drive.

Remember when the rotation was a source of concern? Iwakuma began the season on the disabled list with a torn finger tendon, and while GM Jack Zduriencik wasn’t banking on unreasonable contributions from James Paxton and Taijuan Walker, neither was he expecting the rookies to spend two months apiece on the DL.

The flip side of the first-half injuries to Iwakuma, Paxton and Walker is that by sitting out a collective 192 games, their arms are relatively fresh. Iwakuma resembles the same pitcher who finished third in the 2013 Cy Young vote. Paxton, who was throwing electrifying stuff when he strained his lat muscle in the home opener, is throwing electrifying stuff upon his return.

Walker’s comeback from shoulder impingement has been up and down, but during his most recent performance — Saturday night at Cheney Stadium — the Rainiers right-hander struck out a career-high 13 in seven innings.

Once rumored to be a prized trade-deadline chip going places, Walker is going places with the Mariners. It’s almost certain he’ll be called up in September, if not sooner.

Even as Roenis Elias approaches the proceed-with-caution work limit Zduriencik has imposed on him after 1342/3 innings — no AL rookie has thrown more this season — the Mariners’ staff stands to benefit from addition.

Some of their playoff-race rivals, meanwhile, are dealing with attrition, which is the opposite of addition and suggests that the crazy notion of the Mariners’ surge to obtain the first wild-card spot — worth home-field advantage in a loser-out game — is not so crazy.

The Angels still are the favorites on that front, but a team without any apparent weakness after the trade deadline has lost starter Tyler Skaggs to an elbow injury requiring Tommy John surgery.

Although Skaggs isn’t irreplaceable, he’s a solid back-end-of-the-rotation guy. His absence will put pressure on fellow lefty C.J. Wilson to stand up and deliver quality outings, something Wilson had been struggling to do in six consecutive starts before Tuesday.

While the Angels were learning the bad news about Skaggs, the Tigers were coping with the possibility that arm problems are responsible for the surprisingly mediocre numbers of Justin Verlander.

Verlander is as familiar with trophy-acceptance remarks — he was named AL rookie of the year in 2006, and won both the Cy Young and MVP awards in 2011 — as he is unfamiliar with injuries. The durable right-hander has started at least 30 games every season, without one trip to the DL.

But Verlander didn’t make it to the second inning Monday at Pittsburgh, where manager Brad Ausmus sensed something was awry. Verlander acknowledged soreness in his throwing shoulder, making him the latest injury setback to a staff that already has lost starter Anibal Sanchez (expected to miss three to four weeks with a strained muscle on his side) and presumptive closer candidate Joakim Soria, nursing an oblique strain.

Thanks to Max Scherzer, Rick Porcello and David Price, the Tigers still figure to be a bear of an opponent in a best-of-five division series. But at the rate Joe Nathan is blowing saves — six through Saturday — Detroit’s choke-hold grip on a playoff berth has been reduced to a tenuous handhold.

And then there are the Yankees, who not so long ago feared Masahiro Tanaka’s right elbow injury would deprive them of the rookie sensation until next season. He’s back, in a sort-of, kind-of way. Tanaka is throwing baseballs traveling 90 feet at ground level; his next rehab challenge will be to throw them 120 feet, and then to throw them from a mound.

See him in September? Maybe.

The temptation for Seattle fans is to gloat over the Mariners’ surplus of strong, healthy arms while the Angels, Tigers and Yankees face variously vexing issues.

The temptation is understandable, but don’t forget: Baseball is a day-to-day, minute-to-minute pursuit where fortunes can change if a single wind-up is followed with a wince.

There’s no guidebook on this, and I’m not a doctor, nor an expert on pitching mechanics. All know is what I know, and what I know bodes well for the Mariners and their playoff push.